Maternity mattresses have been proposed in the past, in which the mattress is provided with a cavity in its upper surface, adapted to receive the abdomen of a pregnant woman resting face down on the mattress, so that maximum support may be provided with a minimum amount of discomfort.
One type of maternity mattress has been associated with a normal inner spring bed mattress, in which the coil spring mattress, which is supported on a box spring, is provided with a cavity to receive the abdomen of the pregnant woman. This type of maternity mattress is illustrated in U.S. Pat. No. 4,051,566. To adjust the depth of the cavity in the mattress, an insert is mounted in the cavity and is supported by a power operated mechanism located beneath the bed. Through operation of the power mechanism, the insert can be raised and lowered within the cavity to provide the desired depth of cavity to accommodate the abdomen.
U.S. Pat. No. 4,054,960 describes an inflatable maternity mattress in which the central portion of the mattress is provided with a generally cylindrical opening or cavity to receive the abdomen of the pregnant woman. To adjust the depth of the cavity, air is introduced or exhausted from the mattress. This not only adjusts the depth of the cavity, but also changes the thickness or height of the mattress. Thus, to provide a cavity with a minimum depth, air is exhausted from the mattress to correspondingly reduce the thickness of the mattress to a minimum.
U.S. Pat. No. 4,054,960 also shows an inflatable plug to be inserted within the opening in the mattress when the central cavity is not required.
U.S. Pat. No. 2,089,854 is directed to a maternity cot and mattress, in which the mattress and the supporting cot are provided with aligned openings adapted to receive the abdomen of a pregnant woman. The lower end of the opening or cavity is enclosed by a pair of adjustable straps which are disposed in an X-shaped configuration. By lengthening or shortening the straps through use of a buckle, the depth of the cavity can be adjusted to accommodate various stages of pregnancy.